BACKGROUND: Similar to handedness, hand clasping and arm folding are also lateral preferences.Previous studies showed a variation frequency for hand clasping and arm folding among different populations.OBJECTIVE: To investigate the relationship between patts of lateral preferences (hand clasping or arm folding) and academic performance of middle school students.DESIGN, TIME AND SETTINGS: Cross-sectional investigation. The data were collected in the Beijing Zhongguancun High School in Beijing in May 2007. Data analysis was performed in the State Key Laboratory of Cognitive Neuroscience and Leing, Beijing Normal University during June to July 2007.PARTICIPANTS: A total of 102 senior-grade students from Beijing Zhongguancun High School, including 58 males and 44 females, were selected for this study.METHODS: Different forms of hand clasping and arm folding were recorded. More specifically, hand clasping was either right-thumb-top or left-thumb-top, and arm folding was either right-arm-top or left-arm-top. Students with congruent preference used right-thumb-top-right-arm-top or left-thumb-top-left-arm-top, and incongruent preference was displayed by right-thumb-top-left-arm-top or left-thumb-top-right-arm-top. Academic performances were collected from mid-term exams in six subjects (Chinese, Mathematics, English, Physics, Chemistry, and Biology), with a total points = 100 for each. A three-way (hand clasping, arm folding, and sex) ANOVA was performed to determine the effect on academic performances.MAIN OUTCOME MEASURES: The relationship between hand clasping, arm folding, sex, and academic performance of students.RESULTS: (1) There was no significant difference in distribution frequency between right-thumb-top and left-thumb-top (P > 0.05), or between right-arm-top and left-arm-top (P > 0.05). The distribution frequency difference between boys and girls was not significant for any subtype (P > 0.05). (2) hand clasping had no significant main effect on any of the six subjects (P > 0.05). The right-arm-top students received significantly higher points in Chinese, Physics, Chemistry, and Biology, compared with the left-arm-top students (P <0.05). A significant sexual difference was detected in academic performance in Chinese and English; girls had higher scores than the boys (P < 0.05). The students with congruent preference scored higher in English,compared with those with incongruent preference (P < 0.05).CONCLUSION: The arm folding form of lateral preference had a significant effect on academic performance of middle school students, implying that this human laterality index is of great functional importance.